Imagesetters and platesetters are used to expose media that are used in offset printing systems. Imagesetters are typically used to expose the film that is then used to make the printing plates (also referred to as “plates”) for the printing system. Platemaking systems include platesetters also known as platemakers for directly exposing the printing plates with a laser imaging head.
For example, printing plates are typically pre-cut, various-sized and coated with photosensitive or thermally-sensitive material layers, referred to as the emulsion. For large run applications, the plates are often fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs.
Computer-to-plate printing systems are used to render digitally stored print content onto these printing plates. In a platemaking system a computer system is typically used to drive an imaging engine of the platesetter. In a common implementation, the printing plate is fixed to the outside or inside of a drum or held on a flat bed and then scanned with a modulated laser source in a raster fashion.
The imaging engine selectively exposes the emulsion that is coated on the printing plates with the desired image. After this exposure, the printing plate is typically further processed in machines called processors so that, during the printing process, inks will selectively adhere to the printing plate's surface to transfer the ink to the print medium. Often the post-exposure plate processors include a developer stage for developing the printing plates. Sometimes intervening ovens are used to bake or harden the emulsion before development.
Platesetters are typically used in commercial, production environments. They are used in the manufacture of printing plates for newspapers, books, and magazines, for example. Once imaged and developed, the printing plates are mounted onto large offset printing presses for the printing run.
Since platemakers are used in these commercial environments, metrics, such as initial cost and total cost of ownership, are critical in differentiating between products of various manufacturers. In order to keep the cost to manufacture the machines low, reductions in component costs are often an objective in machine redesigns. Relative to total cost of ownership, machine up-time, average cycle time, and amount of operator intervention required during operation, are very important to the potential buyers of these machines. To decrease the amount of operator intervention in the operation of the platemakers, system manufacturers often provide automation for such jobs as transferring or moving the printing plates to a staging area, to the imaging engine, and from the imaging engine to a developer, stacker or other processing stage.
Often, the cost of the automation accessories are high due to the challenges associated with moving these sometimes very large printing plates without damage or contamination. Thus, it is often not clear from a purely economic standpoint, whether a given owner should purchase the various available automation accessories, because these accessories are expensive and difficult to weigh against the cost to employ operators over the course of the platesetter's lifetime to perform the functions that would otherwise be performed by the automation accessories.
As noted above, one specific area of automation concerns the movement of the printing plates throughout the platemaking system, for example, moving a printing plate from the imaging engine to a stacker, developer, chemical bath, rinser, baking or fixing unit.
In most platemaking systems, the printing plates when ejected from the imaging engine are simply placed on an unload table. An operator must then manually move the printing plates to another location such as a plate stack or plate processor. In contrast, an automated conveyor system receives a printing plate as it is ejected from the imaging engine and automatically moves the printing plate to another location or processor without operator intervention.
Printing plate conveyor systems can be very expensive to manufacture and maintain, typically having many moving parts such as rollers, belts, chains, gears and mechanical linkages. Further, these conveyor systems preferably should include features to change the direction of plate movement. Specifically, since the processor in many environments is located next to the platesetter in order to preserve floor space, the printing plate is consequently ejected from the platesetter along one axis, and must be initially drawn along that same axis by the conveyor, thereafter changing the direction of the movement of the printing plate by 90° to move the printing plate to the processor.
In one example, a printing plate conveyor system includes a conveyor with a series of belts and pulleys for receiving and transporting the printing plate as it is ejected from the imaging engine. Once the plate is completely ejected, a set of rollers extends upward between the pulley belts to pick the plate off of the belts and move the plate in an orthogonal direction to the direction from which the plate was initially ejected.